Bearings and Lubricants
Spherical bearings offer an unequaled combination of high load capacity, high tolerance to shock loads, and self-aligning ability, but they are speed limited. Accordingly, spherical bearings are used in vibrators, shakers, conveyors, speed reducers, transmissions, and other heavy machinery. Although the majority of spherical bearings are made to RBEC-1 tolerances, high-precision grades are available.
Because load-carrying ability is so important, spherical bearings are available in a wide variety of radial thicknesses and axial widths. For a given bore size, double-row spherical bearings are available in five different thicknesses and eight widths. The various combinations of width and thicknesses are designated by series numbers, which range from the very light duty series 39 to the very heavy-duty series 23. Depending on the bore size used for comparison, a series 23 spherical bearing will have a capacity from 3.2 to 5.2 times that of a series 39 spherical bearing.
Single-row barrel spherical bearings have high radial but low thrust capacity. The rollers are symmetric, with modified line contact at both races.
Single-row thrust spherical bearings are made with both symmetric and asymmetric rollers. Each spherical bearing has low radial and high-thrust capability.
Double-row convex spherical bearings have high radial and moderate thrust capacity. Three types of spherical bearings are coded by AFBMA. Type SLB is made with symmetric rollers. Rollers are guided by the pockets of a machined roller-piloted retainer, which is not quite as effective as guidance in the SC and SD types.
The SC design also has symmetric rollers, but rollers are guided by a floating guide ring. The spherical bearing retainer is usually a stamped assembly piloted on the inner ring. As in the SLB, there is modified line contact at both raceways.
The SD bearing uses asymmetric rollers, which reduce skewing tendencies and keep the rollers in contact with the center guide flanges. The overall result is better roller positioning, guidance, and better performance at high speeds.
Double-row concave spherical bearings have characteristics similar to the double-row convex models, but are available in a much smaller range of sizes.